This invention relates to the treating of molten iron. More particularly, the invention relates to the treating materials for nodulizing cast iron.
In the production of gray iron castings, small amounts of certain materials added to the molten iron just before pouring reduces chilling and promotes graphite formation. The common inoculants are graphite or materials having a high silicon content such as ferrosilicon or calcium silicide. To produce the maximum affects, silicon based inoculants require the presence of trace amounts of minor constituents such as aluminum, calcium, barium, strontium, or cerium. The graphite inoculant must be of high purity and highly crystalline.
Formerly, with cupola melting with coke as a fuel, large amounts of sulfur were introduced into the melt. Presently, with electric induction melting, iron with sulfur contents of below 0.04% by weight are common. The low sulfur iron has created a problem in that gray iron having less than 0.04% sulfur content does not readily respond to inoculation with graphite or many ferrosilicon based inoculants because these inoculants are dissolved very quickly at the low sulfur levels. Such phenomena is commonly referred to as "fading".
In a recently developed process of treating iron, the inoculant material is encapsulated within a metal tube in the form of a flexible wire and the wire fed into the molten iron being poured into the casting. However, although this process has greatly reduced the fading affect to an extent that high silicon content ferrosilicons can be used to inoculate the molten iron, the less costly graphite inoculant still tends to dissolve too quickly for effective inoculation in low sulfur irons.